Humans are creatures of habit , we need regular sleep cycles , but you can condition yourself to be able to sleep intermittently ( like a cat ) , 10 min here , 15 min there , throughout the day , even tho its not natural for us to do so . What I dont like is what I call ” blinking ” . Thats when you fall asleep for a very short amount of time , then wake up , like a long blink of the eyes . Your not sure how long you fell asleep , but you know you did it . I used to commute for work between two cities , long boring drive with nothing to see but sh*t desert . After working all day in the heat , the nice cool truck on that drive home made me blink ……………….more than once , I guess it was only for about 5-7 secs , 10 at the most ………….but it scared me awake for the rest of the drive . That brings up another factor , some temps can make you more vulnerable than others to that . Being a Southwesterner , I understand heat very well I also had a job for 25 years , traveling all over the US , exposed to all the different weather conditions in the country . Heat will make you more tired than cold as a general rule . Humid heat gives you more warning than dry heat , dry heat sucks the life out of you faster than you will be aware of . Temps affect your sleep requirements .